Call post_create_inferior in ctf_open.

We don't call post_create_inferior at the end of ctf_open.  It is an
oversight in patch

  [PATCH 2/2] Create inferior for ctf target.
  https://sourceware.org/ml/gdb-patches/2014-01/msg01056.html

This patch is to call post_create_inferior at the end of ctf_open,
like the end of tfile_open.

gdb:

2014-04-19  Yao Qi  <yao@codesourcery.com>

	* ctf.c (ctf_open): Call post_create_inferior.